1. Field of the Invention
The present invention generally relates to an apparatus and method for utilizing energy, such as radio frequency (RF) energy, to treat defined areas of tissue and more particularly to ablate tumors with RF energy through the use of a needle having a spreading array of individually traversing conductive tines which are independently positioned and activated.
2. Description of Related Art
Radio frequency energy has been used in medical procedures for many years for the treatment of soft tissue. Radio frequency ablation occurs from a high frequency alternating current flowing from the tip of an electrode through the surrounding tissue. Ionic agitation is produced in the tissue around the electrode tip as the ions attempt to follow the change in direction of the alternating current. This ionic agitation creates frictional heating of the tissue around the electrode. Thus, similar to a microwave, the tissue heats even though the electrode does not; although conducted heat may progress back to the electrode from the surrounding tissue. The heat generated results in local cell coagulation and necrosis. Coagulated cells die and thus cease dividing. This technology has been used for example in the treatment of unresectable hepatic cancer.
RF ablation may be performed through an open abdominal incision or via laparoscopy which is performed through multiple, small skin incisions. If indicated, RF ablation can also be conducted percutaneously through small skin incisions. The duration of the procedure depends on many factors, including the number of applications desired and the location of the tissue to be treated. Typically, the procedure will be performed in a surgical suite where the patient can be monitored by imaging equipment.
RF ablation has had very promising results in the treatment of hepatic cancer. Using devices in the prior art, the procedure, however, takes a considerable amount of time, approximately 15 minutes for every 4 centimeters of tumor after the needle has been placed in the patient and the tines fully deployed. A clinical investigation of RadioTherapeutics is discussed in Curley et al., Radiofrequency Ablation of Unrectable Primary and Metastatic Hepatic Malignancies, 230 ANNALS OF SURGERY 1 (1999), which is incorporated herein by reference in its entirety.
A device that is currently on the market, the “LeVeen Needle Electrode” by RadioTherapeutics Corporation, deploys an umbrella of 10 tines which burrow into the tumor growth distributing the RF energy thereby heating and destroying the cells. Following the procedure, the body reabsorbs the destroyed cells over a period of time. Structurally, the LeVeen Needle Electrode consists of ten evenly spaced wires that are deployed through an insulated metal cannula. When deployed, the array of wires advances through the tissue in a constant radius curve away from the metal cannula, producing the umbrella shaped design of the LeVeen Needle Electrode. The cannula supports the array which is deployed within its predetermined shape and dimensions. According to marketing literature, this allows penetration of the tissue irrespective of density. Thus, the wires of the LeVeen Needle Electrode supposedly can be deployed into tissue which is hard, such as calcified tissue in its entirety. RadioTherapeutics marketing literature also states that U.S. Pat. Nos. 5,827,276, 5,855,576, and 5,868,740 describe the Le Veen Needle, each of which is incorporated herein by reference.
FIG. 1 depicts one version of the Le Veen Needle 20 in accordance with the prior art which includes insertion device 22 electrically connected to a radio frequency generator 24. The radio frequency generator 24 includes at least one active terminal 26 and a return terminal 28 with ground plate 30 electrically connected by conductor 32 to terminal 28. Insertion device 22 is comprised of a plurality of electrically conductive wires 34 which are bundled at a proximal end and connected to terminal 26 to conduct RF current therefrom. Wires 34 are threaded through an electrically insulated or non-conductive tube or catheter 36.
As shown in FIG. 1, a 10-wire array 38 is formed with each wire 34 arching from catheter 36 in a general “U” shape with each wire substantially uniformly separated. Thus, array 38 is formed of a plurality of wires 34 curving radially outwardly from the axis of distal end 36a of catheter 36. Wires 34 all extend a length such that, when fully extended past catheter distal end 36a, a portion of each wire 34 is perpendicular to the axis of tube 36 and which continue to curve back and up such that wire distal ends 34a are oriented generally parallel to the axis of the tube distal end 36a. Wire distal ends 34a thus remain uniformly deployed and separated within a plane orthogonal to the tube distal end 36a. 
In addition, use of the LeVeen Needle Electrode creates a roughly spherical lesion which is approximately equal to the diameter of the fully deployed wire array. Thus, a 3.5 cm LeVeen Needle Electrode will produce a thermal lesion approximately 3.5 cm in diameter. RF energy radiates from individual array wires into adjacent tissue in a 360 degree pattern. Each wire is also connected to the same power source. The energy level, and thus the heating effect, falls off rapidly at increasing distance from the individual wires. The highest temperature will therefore always be created immediately adjacent to the wires. In addition, tissue heat can be conducted up a short distance of the cannula which results in a slight peaking of the thermal lesion around the cannula. This results in a thermal lesion which is spherical around the tines of the array and slightly sloped up the shaft of the cannula. The center of the spherical lesion is centered on the array and therefore slightly offset distally from the end of the cannula.
The major disadvantage of such devices is that the tines cannot be adjusted individually to fit the volumetric dimensions of the tumor or tissue area to be treated. Each tine must be deployed or withdrawn concomitantly. Thus, if a tumor is irregularly shaped, the device may have to be inserted several times at different locations and at different depths in order to treat the entire volume of tissue. This increases the time to perform the procedure as well as increasing the risk of patient complications.
RadioTherapeutics literature also indicates that the RF generator used in conjunction with the Levine Needle was designed to respond to changes in tissue impedance and to detect changes in bulk tissue impedance throughout the target volume of tissue. Controlled application of RF energy from a shaped array with many wires allegedly causes relatively uniform desiccation of the tissue with a subsequent increase in tissue impedance. The rise in impedance that occurs following the application of power for a designated period of time indicates that thermal ablation has occurred. One disadvantage, however, is that the tissue treated tends to overheat too quickly thereby destroying the cells and desiccating the area immediately surrounding each tine. When this occurs, impedance is greatly increased and flatlines. Once the impedance level flatlines, depth ablation is no longer possible and the affective zone is moved proximally along the tine toward the cannula or in conventional LeVeen needle technology goes to a tine with the least resistance. Once the small area surrounding the needle is completely desiccated, the needle must be repositioned which again increases procedural time and the chance of patient complications. RF generators, such as the RF 2000 Radiofrequency Generator, by RadioTherapeutics Corporation, is described in U.S. Pat. Nos. 5,817,092, 5,827,276, 5,855,576, and 5,868,740, each of which is incorporated herein by reference in its entirety.